But Kerry, speaking at Asia-Pacific foreign ministerial talks in the tiny petro-state of Brunei, said after a meeting with his Chinese counterpart that the two Pacific powers were united in their opposition to North Korea's nuclear drive.
A year after a US-backed push for a South China Sea code of conduct broke down acrimoniously, this year's hosts Brunei have instilled a more cordial tone, with China agreeing yesterday to hold talks on establishing such a code.
Overlapping claims to the South China Sea loom as a flashpoint, with China claiming virtually all of the body of water, drawing accusations from rival claimants the Philippines and Vietnam that it is mounting a creeping takeover of disputed islets.
ASEAN members Brunei and Malaysia, as well as Taiwan, also claim parts of the sea.
Beijing asserts the South China Sea is not Washington's concern, but Kerry insisted the United States saw a "national interest" in ensuring freedom of commerce in a waterway vital to world trade.
Yesterday, Philippine Foreign Secretary Albert Del Rosario told his ASEAN colleagues that China had begun a "massive" military build-up in the sea and its actions "pose serious challenges for the region as a whole".
China has been reluctant to reach a code of conduct with the ASEAN bloc, preferring to negotiate individually with each country.
Last year's talks in Cambodia -- a Beijing ally -- ended without a joint statement for the first time due to intra-ASEAN acrimony over the issue.
"Our actions are not intended to contain or to counterbalance any one country," he said.
North Korea defiantly carried out its third nuclear weapons test in February and threatened to attack the United States in language that was shrill even by the standards of the reclusive communist state.
